In medical imaging, image registration and fusion is now being used to align images from different modalities (or 2D and 3D images from the same modality) to bring additional information into the display of information from a modality. An example is the fusion of PET (positron emission tomography) or SPECT (single photon emission computed tomography) images showing tumor information, but little else, with CT (computed tomography), showing detailed anatomy. Another approach, which has gained attention lately, is 2D-3D registration: the registration of pre- or intraoperative 3D volume rendered data to intraoperatively acquired fluoroscopic or angiographic images.
One application of the registration technique is the navigation of a device, which can be visualized in the real-time 2D fluoroscopic image, using the information given by the 3D volumetric rendering, e.g. navigating a needle (seen in the fluoroscopic image) to a tumor (seen in the registered 3D volumetric image but not in the fluoroscopic image). However, the overlay of 2D and 3D images has no depth information so that navigation of a device may be difficult. The device can presently be navigated by viewing the device from several angles in fluoroscopic images. However, in addition to increasing the radiation does to the patient, this requires the movement of the C-arm of the X-ray device during the intervention.